Metal container suitable to accommodate a heating or cooling component method and for manufacturing it

ABSTRACT

A method of producing a metal container from a low carbon steel strip or sheet coated on at least one of its surfaces with a coherent laminated coating of a thermoplastic polymer material includes one or more redrawing stages which reduce the thickness of the side walls by a drawing/stretching operation, and a partial reverse redrawing stage to produce an initial internal chamber whose depth is produced by a reduction of its height. The initial internal chamber is then redrawn to produce two chambers of differing diameter and depth, the diameter of the initial chamber being decreased by the redraw operation and inserting by base reforming the final chamber with a new internal diameter and depth produced by a reduction in the container height.

The invention relates to a metal container and its manufacture. Themetal container comprises a plurality of internal chambers of variousdepths and diameters, the design of which can be varied dependent on therespective application. The internal chamber or chambers may be filledwith appropriate substances and used to heat or cool via a chemicalreaction the contents of another chamber. The container according to theinvention can thus be used to accommodate a heating or cooling componentto heat or cool the contents, although it could also be used foralternative applications, e.g. where food products need to be keptseparate.

This invention also relates to a method of manufacturing such a metalcontainer, incorporating a combination of internal chambers, suitable toaccommodate a heating or cooling component, used for heating or coolingits contents.

The method of manufacture used in producing the metal container mayinvolve a combination or a series of the following processes, cupping,draw redraw (DRD) and/or draw stretch redraw (DSRD), reverse (partial)redraw, redraw of the reverse chamber and base reform depending onapplication and container size. Examples of such methods are disclosedin U.S. Pat. No. 5,088,870 and WO 99/61326.

For a typical design the process developed is as follows: The originalcup is redrawn in sequential stages until a container of correctdiameter is produced. The container is then subjected to a reverse(partial) redraw in order to insert an internal chamber. The next stageinvolves redraw of the internal chamber, hence producing two internalchambers of different diameter and depth. The final chamber is producedby means of base reform which produces a container of correct externaldiameter and height and, hence, a finished container of correct internalchamber diameters and depths.

For this invention, the configuration of internal chambers of the metalcontainer consists of three internal chambers, with the followingtypical dimensions: 61.6 mm diameter at 4 mm deep, 53.7 mm diameter at15 mm deep and 45 mm diameter at 73 mm deep. The starting material isconventionally a double reduced product of high strength high ductilitylow carbon steel with a proof strength of 480-720 N/mm², and coated witha polymer coated film on one or each surface. The use of DR products forthe metal container is not exclusive to the design, as it is possiblethat a range of SR tin mill products can be used for the application.

This invention concerns a method of producing a typical metal containerused to accommodate a heating or cooling component, used in the heatingor cooling of the contents of the metal container.

The feed stock for the method of manufacture for the metal containers tobe produced in accordance with the invention is a double reduced highstrength high ductility low carbon steel with a proof strength of480-720 N/mm². The maximum carbon level for the steel is typically 0.05%by weight. A typical specification for this steel is by weight %: C0.01-0.04; S 0.02 max.; P 0.015 max.; Mn 0.15-0.30; Ni 0.04 max.; Cu0.06 max.; Sn 0.02 max.; As 0.01 max.; Mo 0.01 max.; Cr 0.06 max.; A0.02-0.09 and N 0.003 max. The steel is reduced by hot or cold rollingto a gauge typically of between 0.12 mm and 0.30 mm and is processed byknown appropriate heating cycles and continuous annealing. The steel hasa minimum earing quality.

As an example, the feed stock used is DR 580 CA 0.24 mm, coated with aPET laminate coating of 0.025 mm (white) on one side and a PET laminatecoating of 0.020 mm (clear) on the other.

The specification for this steel is by weight %: C 0.012-0.04; S 0.02max.; P 0.015 max.; Mn 0.15-0.30; Al 0.025-0.055 and N 0.003 max., plustrace elements: Ni 0.04 max.; Cu 0.06 max.; Sn 0.02 max.; As 0.01 max.;Mo 0.01 max.; Cr 0.06 max.

Strip produced from the feed stock is subjected to an electrolyticcoating process. In this process, the steel strip is cleaned and pickledbefore being passed through a plating bath in which it is coated with athin layer of chromium metal, typically of 0.010 mm thickness followedby a thin layer of chromium oxide, again typically of 0.010 mmthickness. Alternatively, tinplate or other suitable substrate could beemployed.

The strip is then coated with a polymer material. In this process alayer of PET (polyethylene terephthalate) and/or PP (polypropylene) isbonded to the surface of the metallic coated steel strip or sheet usingheat and pressure.

The films are co-extruded so that the bonding layer of 0.002 mm firstmakes contact with the steel and forms a strong bond. After the bond isformed with the substrate the polymer films are melted and held abovethe recrystallisation temperatures for a few seconds before beingrapidly quenched to below their softening temperatures.

This produces an amorphous structure in the PET and a minimalcrystalline structure in the PP. The method of coating the strip can bea direct extrusion or laminating process. Typically the thickness of theexternal polymer is in the order of 0.025 mm thickness and the internalpolymer is between 0.015 and 0.030 mm. Laminating processes and polymerfilms of a different structure and composition other than thosediscussed may be employed.

Cupping

The strip, either in sheet or coil form is fed to a cupper in apre-waxed condition or is passed through a waxer on entry to the cuppingsystem. The wax may be edible and petroleum based with film weights inthe range 5-20 mg/ft². Discs are stamped from the sheet or strip. Thecup is drawn in one operation using a die with a diameter typically inthe range 150 mm to 300 mm.

This diameter is dependent (with gauge) upon the required can size andtype of application. The draw ratio (i.e. ratio of the diameter of thedisc to that of the cup) is typically in the range 1.0-2.0:1. Thegeometry of the tooling is designed in combination with the correctblank holding load to give a reduction in wall thickness at the cuppingstage of up to 20%, however this can be produced with a smaller orgreater reduction depending on application.

This is accomplished with a die radius typically between 0.5 mm and 6.5mm and a parallel land length of up to 10 mm. The blank holding load isachieved by use of a boosted air pressure of up to 200 psi fed into aseries (typically three) of internal multiplying pistons. The punch/diegap is important and is controlled by the feed stock gauge and coatingand gaps of 1.20-2.50 times the starting total laminate thickness aretypically used.

The punch nose radius is carefully controlled to achieve the requireddraw/stretch whilst minimising subsequent can wall marking which couldlead to laminate rupture. Punch nose radii in the range of 0.5 mm to 10mm are generally required.

First Redraw Processing

The cupper cup is passed into the draw/stretch redraw press whichcontains tooling for both first and second redraw operations. Thediameter of the cup is reduced in the first redraw operation with a drawratio in the range 1.0-1.7:1, and with a wall thickness reductiontypically 25% of the in going cup wall thickness, however this can beproduced with a smaller or greater reduction (in the range of 10-60%)depending on application.

The wall thickness reduction is achieved by a stretching technique. Thewall thickness reduction is balanced with the draw ratio and is achievedby use of pressure sleeve and die geometry in combination withcontrolled blank holding loads.

The tooling geometry typically is as follows: pressure sleeve diameterup to 0.66 mm smaller than the cupper cup internal diameter; pressuresleeve radius up to 2.0 mm; die radius up to 2 mm with a parallel landlength up to 5 mm.

The blank holding load is achieved by use of air pressure of up to 100psi fed into a stack of two or more internal multiplying pistons.

Location of the cup on the die is effected by means of a nest recesswith a diameter matched to the cupper cup, allowing for the thickness ofthe actual laminate. The radius of the nest diameter with the die at thebase of the nest is in the range 0.10-2.00 mm.

The punch is parallel along its length and the gap between the punchdiameter and die (per side) is generally controlled to between 1.20 and1.50 times the starting laminate thickness. The punch radius isimportant to achieve the required stretch whilst minimising subsequenten wall marking which could lead to laminate rupture. Punch nose radiiin the range 1 mm to 3 mm are typically used.

Second Redraw Processing

The first redraw cup is passed back into the stretch redraw press astation containing the second redraw tooling. The cup diameter isreduced in this operation to the final metal container diameter,typically 211, however, may vary depending on application. The drawratio is generally in the range 1.0-1.7:1, and with a wall thicknessreduction typically 25% of the ingoing cup wall thickness, however thiscan be produced with a smaller or greater reduction (in the range10-60%) depending on application.

The wall thickness reduction is again achieved by a stretching techniqueusing a combination of pressure sleeve and die geometry with controlledblank holding loads. The correct choice of diameter reduction ratio toachieve the finished can is also important in enabling the stretchprocess to be successful. The tooling geometry used typically is asfollows: pressure sleeve diameter up to 0.30 mm smaller than the firstredraw cup internal diameter; pressure sleeve radius up to 2.0 mm; dieradius up to 2 mm with a parallel land length up to 5 mm.

The blank holding load is achieved by use of air pressure of up to 100psi fed into a stack of two or more internal multiplying pistons.Location of the cup on the die is effected by means of a nest recesswith a diameter matched to the cupper cup, allowing for the thickness ofthe actual laminate. The radius of the nest diameter with the die at thebase of the nest is in the range 0.10-2.00 mm.

The punch is parallel along its length and the gap between the punchdiameter and die (per side) is generally controlled to between 1.00 and1.20 times the starting laminate thickness. The punch radius isimportant to achieve the required stretch whilst minimising subsequentcan wall marling which could lead to laminate rupture. Punch nose radiiin the range 1 mm to 3 mm are typically used.

Gap control or arrested draw is employed at the redraw stages toeliminate high spot clip off or the generation of laminate “whiskers”.When gap control is used, gaps of 0.10 to 0.15 mm between the pressuresleeve and die face are generally used depending upon the laminate feedstock used. The overall metal container wall thinning employed is 5-40%dependent upon the end use of the container.

The second redraw container (i.e. final container diameter) istransferred to a different redraw press, which can accommodate toolingfor the reverse draw for the internal chamber, redraw of the reversechamber and base reform operations.

Reverse Draw Operation

The container undergoes a reverse draw operation, in order to produce aninitial internal chamber. The draw ratio for the initial internalchamber is generally in the range 1.0-1.7:1, with no (or limited) wallthickness reduction instead the internal depth is achieved by areduction of the in going second redraw container height. To preventwall thickness reduction correct choice of die radius, punch radius andcontrolled blank holding pressure are required. The tooling geometrytypically is as follows: die external diameter up to 0.60 mm smallerthan the second redraw can internal diameter; die external radius up to2.0 mm; die radius up to 5 mm with a parallel land length up to 5 mm.

The blank holding load is achieved by use of air pressure of up to 100psi fed into a stack of two or more flexible pressure chambers. Locationof the container on the pressure sleeve is effected by means of a nestrecess with a diameter matched to the second redraw can, allowing forthe thickness of the actual laminate. The radius of the nest diameterwith the die at the base of the nest is in the range 0.10-2.00 mm.

The punch is parallel along its length and the gap between the punchdiameter and die (per side) is generally controlled to between 1.10 and1.40 times the starting laminate thickness. The punch radius isimportant to prevent 1 limit wall thickness reduction, instead it isused to draw the container wall to produce the internal chamber. Thepunch nose radius in the range 2 mm to 7.5 mm is typically used, Depthof the reverse draw is controlled out by the means of a mechanical stop.The depth of the reverse draw is dependent on the application, typicallybetween 10-100 mm.

Redraw of the Reverse Chamber

The reverse redraw container is transferred to the next operationstation, where redraw of the reverse chamber is performed. Thecontainer's internal chamber is redrawn to a smaller diameter for aportion of it's depth, i.e. two different chamber diameters and depths.The draw ratio used in the reduction of the internal chamber isgenerally in the range 1.0-1.7:1. The increase in height of the internalchambers is caused by a reduction of the reverse redrawn can basediameter and base thickness reduction.

Base thickness reduction is again achieved by a stretching techniqueusing a combination of pressure sleeve, punch and die geometry withcontrolled blank holding loads. The correct choice of internal diameterreduction ratio to achieve the required internal parameters is importantin enabling the process to be successful.

The tooling geometry used typically is as follows: die external diameterup to 0.60 mm smaller than the second redraw can internal diameter; dieradius up to 5 mm with a parallel land length up to 5 mm.

The blank holding load is achieved by use of air pressure of up to 100psi fed into a stack of two or more flexible pressure chambers. Locationof the container on the pressure sleeve is controlled by means of theinternal chamber from the reverse redraw operation with a diameter 0.60mm smaller than the internal chamber for can location, allowing for thethickness of the laminate to be taken into account.

The punch is parallel along its length and the gap between the punchdiameter and die (per side) is generally controlled to between 1.10 and1.40 times the starting laminate thickness. The punch radius isimportant to achieve the required stretch. The punch nose radii in therange 2 mm to 7.5 mm is typically used.

Depth of the redraw is controlled by the means of a mechanical stop. Thedepth of the redraw operation is dependent on the application, typicallybetween 10-100 mm.

Base Reform

The redraw container is transferred to the final operation station forthis application, where base reform is performed. The final internalchamber is reformed to the largest diameter chamber for a specifieddepth (i.e. three different chamber diameters and depths). The drawratio used in the reduction of the internal chamber is generally in therange of 1.0-1.4:1; with no wall thickness reduction, instead theinternal depth for this final chamber is achieved by a reduction fromthe ingoing second redraw container height.

To prevent wall thickness reduction, a correct choice of die and punchradius is required. The tooling geometry typically is as follows: punchexternal diameter up to 0.60 mm smaller than the second redraw caninternal diameter; punch external radius up to 2.0 mm; punch internalradius up to 2.0 mm; die radius up to 2.0 mm with a parallel land lengthup to application requirement;

The base reform load is applied by the reaction between the punch anddie that is used to apply the base design.

Location of the container on the die is effected by means of a nestrecess with a diameter matched to the second redraw container, allowingfor the thickness of the actual laminate. The radius of the nestdiameter with the die at the base of the nest is perpendicular.

Depth of the redraw is controlled by the means of a mechanical stop. Thepunch bottoms out on the die face at the specified depth for theapplication requirements.

After the final operation the container is trimmed (this can occur afterthe second redraw operation) and passed through an oven. This oven istypically held at 200-230′ C and the pass time is typically between 1and 3 minutes. This facilitates the removal of petroleum wax lubricantto such a level so that it does not interfere with the lay down ofprinting inks used to decorate the can. It also raises the surfaceenergy of the PET coating to at least 38 dynes/cm, which increases thewettability of the PET surface to printing inks. The temperature cyclein the oven is chosen to minimise recrystallisation of the PET by rapidtemperature rise and cooling cycles.

Printing is currently carried out using conventional machinery, whichapplies thermally curing inks onto the external surface of the can.Again, recrystallisation of the PET is minimised as above.Alternatively, a shrink wrap sleeve may be applied at lowertemperatures.

The invention will now be further described with reference to theaccompanying diagrammatic drawings, in which:

FIG. 1 illustrates five stages of a cupping operation of the method ofthe present invention;

FIG. 2 illustrates five stages of a first draw 1 stretch redrawoperation of the method of the present invention;

FIG. 3 illustrates five stages of a second draw/stretch redraw operationof the method of the present invention;

FIG. 4 illustrates six stages of a reverse redraw operation of themethod of the present invention;

FIG. 5 illustrates six stages of a redraw operation of the method of thepresent invention;

FIG. 6 illustrates five stages of a base reform operation of the methodof the present invention;

FIG. 1 shows five stages of a cupping operation of the method of thepresent invention. The five stages are labelled A to E. Stage 1A shows afeed stock strip 1 of laminated steel strip held between a draw pad 2and a blank and draw die 3. A disc of the required diameter is cut fromthe strip, by downward movement of a cutter 5 (see FIG. 1B). A punch 6(FIGS. 1C and 1D) is then moved downwardly with the disc edges trappedbetween the opposed surfaces of the draw pad 2 and draw die 3. A cup 7is thereby formed which is removed from the die by air pressure (seeFIG. 1E).

As will be seen from FIG. 2, the cup is then placed on a die for firstredraw purposes. This stage is illustrated in FIG. 2A. The die is formedwith a shaped lip 9 and has a curved annular projection 10 protrudinginwardly from its upper surface. As seen in FIG. 2B, a pressure sleeve11 and punch move downwardly and within the side wall of the cup 7. Theouter rim of the cup base seats between the opposed surfaces of thepressure sleeve 11 and the die 8. The gap between these members issufficient only to restrict movement of the cup 7, not to impose a forcesufficient to deform or iron the cup. As the punch is moved downwardly,so the cup wall is stretched to increase the cup height.

This stretching process can be seen more clearly from FIG. 5. It will beseen that the cup wall between the projection 10 and the punch lowerface is not in contact with either the die 8 or the side wall of thepunch 12. Movement of the cup between the pressure sleeve 11 and the die8 and over the curvilinear projection 10 is restricted to causestretching of the cup wall. After stretching, the cup is ejected by airpressure (see FIG. 2E).

Turning to FIG. 3, the second redraw operation uses the same or similarpressure sleeve and die as those used in the first redraw operation.These have been accordingly been given the same numerical reference. InFIG. 3, the cup 7 is again shown in positioned on the die 8, see FIG.3A. The pressure sleeve 11 is moved downwardly as shown in FIG. 3B toposition the sleeve within the cup 7. Again, the spacing between thesleeve 11 and the die 8 is to restrict movement of the cup, not topreclude such movement. A punch 14 is moved downwardly into engagementwith the cup base to once again stretch the cup side wall and effectelongation thereof. This stretching operation being as described abovein relation to FIG. 2. This stretching operation is shown in FIGS. 3Cand 3D. The fully stretched and formed cup is ejected by air pressure(see FIG. 3E).

FIG. 4 concerning the reverse redraw operation illustrates how theinitial internal chamber is applied. Cup 7 is placed on the pressuresleeve 15 for the reverse redraw for the initial internal chamber. Thisstage is illustrated in FIG. 4A. As seen in FIG. 4B, the die 14 movesdownwardly and locates in the cup 7. The die 14 continues its downwardmovement and clamps the cup 7 between itself and the pressure sleeve 15,see FIG. 4C. The die 14 continues the downward motion, and in doing so,forces the pressure sleeve 15 to move in the same direction, hence,causing the cup 7 to be drawn over the fixed punch 16, resulting areduction in the height of the second redraw cup (i.e. material is notthinned, but moved to new position, due to minimal blank holdingpressure to be applied). The depth of the internal chamber is controlledby a mechanic stop at a described displacement. This operation appliesthe initial internal chamber, see FIG. 4D. The die 14 begins its upwardmotion as illustrated in FIG. 4E. After the reverse redraw operation thecup 7 is ejected by air pressure, see FIG. 4F.

In FIG. 5, the redraw of the initial internal chamber is illustrated,which produces two internal chambers of different diameters and depths.Cup 7 is placed on the pressure sleeve 18 for the redraw of the initialinternal chamber. This stage is illustrated in FIG. 5A. As seen in FIG.5B, the die 17 moves downwardly and locates in the cup 7. The die 17continues it downward movement and clamps the cup 7 between itself andthe pressure sleeve 18, see FIG. 5C. The die 17 continues the downwardmotion, and in doing so, forces the pressure sleeve 17 to move in thesame direction, hence, causing the cup 7 to be drawn over the fixedpunch 19. As the die 17 moves downwardly the cup base is reduced indiameter, producing two internal chambers of different diameters anddepths, see FIG. 5D. The depth of the internal chamber is controlled bya mechanic stop at a described displacement. The die 17 begins itsupward motion as illustrated in FIG. 5E. After the reverse redrawoperation the cup 7 is ejected by air pressure, see FIG. 5F.

FIG. 6, describes the process of base reform, this is whereby the finalinternal chamber (for this application) is applied to the can. In FIG.6, the cup is located in the die 21 for the base reform operation tooccur see FIG. 6A. As seen in FIG. 6B, the punch 20 moves downwardly andlocates in the cup 7. The punch 20 continues it downward movement intoengagement between the cup 7, itself and the die 21. With the thirdrecess applied, due to a reduction, once again, from the ingoing cupheight, as explained in relation to FIG. 4. This base reform operationis shown in FIGS. 6C and 6D. The punch 20 begins its upward motion, andthe fully formed cup 7 is ejected by air pressure, see FIG. 6E.

It will be appreciated that the foregoing is merely exemplary of methodsand apparatus in accordance with this invention and that modificationscan readily be made thereto without departing from the true scope of theinvention.

The advantage of such a two piece can over the three piece version isthat there is no seaming of the heat exchange unit to the weldedcylinder, which removes the problem of corrosion encountered at theseaming of the cylinder to the heat exchange unit.

1. Method of producing a metal container from a low carbon steel stripor sheet coated on at least one of its surfaces with a coherentlaminated coating of a thermoplastics polymer material in which a blankproduced from the coated steel strip of sheet to a drawing operation toproduce a cup, the method being comprised of the following steps: (i)subjecting the cup to at least one drawing and stretching operation toreduce the thickness of the cup wall and to increase the cup heightwithout ironing of the wall surface; (ii) subjecting the stretched cupto at least on partial reverse redrawing operation to produce within thestretched cup a first internal chamber whose depth is produced by areduction of its height without any reduction in wall thickness; (iii)subjecting the first internal chamber to a reverse redrawing operationto produce a second internal chamber whose diameter and depth differsfrom those of the first internal chamber; and (iv) subjecting the cupbase to a reforming operation to produce a third internal chamber whosediameter and depth differ from those of the first and second chamber andwhose depth is produced by a reduction in the cup height.
 2. Methodaccording to claim 1 wherein the thermoplastic polymer has goodformability and comprises an internal coating which prevents corrosionof the container by its contents and an external coating which preventscorrosion of the container by its heating/cooling solution, the laminatecoating being applied to the metal surface by means of direct extrusionor lamination.
 3. Metal container produced by a method as claimed inclaim 1 having a combination of internal chambers of differing depthsand diameters.
 4. Metal container as claimed in claim 3 produced from adouble reduced high strength high ductility low carbon steel having aproof strength in the range 490 to 720 N/mm.
 5. Metal container asclaimed in claim 3 wherein the maximum carbon level for the steel is0.050% by weight.
 6. Metal container as claimed in claim 4 wherein thesteel comprises by weight %: C 0.01-0.10; S 0.02 max.; P 0.015 max.; Mn0.15-0.30; Ni 0.04 max.; Cu 0.06 max.; Sn 0.02 max.; As 0.01 max.; Mo0.01 max.; Cr 0.06 max.; Al 0.02-0.09 and N 0.003 max.
 7. Metalcontainer as claimed in claim 4 wherein the steel is reduced by hot orcold rolling to a gauge of between 0.12′ mm and 0.3 mm.